Nice. Thyatrons were about the only component available for high-power control in the tube era. Today we have MOSFETs which approach ideal power switches, but it took a long time to get there.
As someone pointed out, that's a switching voltage regulator, not a switching power supply. The transformers there are all upstream of the switching.
I've restored five Teletype machines like the OP's Model 19 [1], so I've needed similar 120VDC 60mA power supplies. So I designed my own switching power supply.[2] This has a USB port for input, and a 120VDC 60mA output for directly driving the Teletype machine. It's powered entirely from the USB port.
This seemed impossible to some people. There's only 5V at less than 500mA coming in, and 120VDC 60mA out. But it's not impossible, because the load is inductive and intermittent. The selector magnet in old Teletypes has a huge inductance, about 5.5 Henries. (Not mH, H.). The 120VDC is only needed for about the first 1ms of each bit time, to force current through that huge inductance. By 5ms or so, you only need about 6V. So you can charge up a capacitor to get the initial 120V, then let a sustain supply take over.
My design is totally modern, built from surface mount components and in a small case.
Here's the schematic.[3] There's an explanation in [2].
It's been amusing to see the reaction of
the Teletype community. They like it, but most can't solder surface mount. One hobbyist is making
these things for others. I put the design on Github as open source and made a few for myself, and
I've sold some board kits. Not enough potential volume to have it manufactured.
Informally, here's how a switching power supply works. Everywhere else in electronics, you try to get rid of spikes. In switching power supplies, you make and use big ones. You start with a source of DC power, and you hook that to the primary winding of a transformer, with a switch so you can turn the power on and off. You turn the switch on, and current flows into the transformer. The magnetics in the transformer charge up, storing energy. After a while (milliseconds) the magnetics will saturate, and can't store any more energy. You now have a short circuit, DC going through a low-resistance transformer. But you turn off the switch before that happens. (Switching power supplies are always milliseconds from burnout, which is why they burn up if the switching fails.)
When you turn the switch off, you now have an open circuited inductor. The energy in that inductor has to go someplace. It comes out as a huge spike, in theory infinite voltage if the transformer resistance was zero, and in practice it can be a few hundred volts. It can't come out the primary, because the switch is open. So it comes out the transformer's secondary winding, where it's fed through a diode into a capacitor. There's the output.
It's simple. An old-style auto ignition with a coil and breaker points works this way. The problems come in as you make it well-behaved. First, controlling the switch is complicated. You want to open the switch before the transformer hits saturation. Failure to do this will burn something out. So there's usually current sensing. Then you want to turn the switch back on when the output voltage from the inductor drops below the voltage in the output capacitor, because no more current will flow through the diode after that.
That just makes it output power. Then you need output voltage sensing, which shortens the charging time to reduce output to maintain the desired voltage. You need protection to shut everything down if the switch gets stuck. (MOSFETs tend to fail in the ON state, and lack of good protection circuitry causes fires.)
This thing works by making big spikes at a few hundred kilohertz. That makes it a radio transmitter. You need inductors and bypass caps to prevent it from blithering all over the RF spectrum. Or sending spiky noise to its output or input. The bypass caps and inductors need to be close to the source of the spikes, so PC board layout really matters. These things will not work on a breadboard.
All this is why switching power supplies have so many small parts. Once you get it right, they work beautifully. Very high efficiency and low heat.
That reminds me of a funny story. The windmill I built worked well in medium and high winds, but did nothing but spin idly when the wind was low. Still, that's (a little) energy that you could capture in theory but it simply did not have enough voltage to get over the battery terminal voltage which makes it impossible to charge the battery.
But a windmill is mostly coils and magnets and when you short it it actually will charge the battery, briefly robbing the blades of some momentum. So, if you periodically short the coils using a bunch of powerfets and an oscillator you can charge a windmill in low wind conditions that would otherwise do nothing.
So far so good. Built it, tested it, worked like a charm. And then one day I decided to temporarily decouple the windmill from the switchboard, but I had forgotten about that little booster. FOOM, instant fire on the booster board after I pulled the switch. The FET circuitry and the oscillator had happily continued to work on the power provided by the windmill, and had allowed the end stage of the circuit to reach a very large multiple of the voltage that it normally dealt with because the battery kept the voltage pegged to a maximum of about 48V!
Needless to say that led to a somewhat more robust V2...
What you've built here is a rudimentary boost converter, using the motor inductance as your inductor, and your battery as your output capacitance.
The next step up here is to build a controllable device that can implement maximum power point tracking; a buck-boost power topology might be what you're looking for here.
Note that MPPT on a wind turbine is more difficult than, say solar, because the rotor speed is another state variable to consider. A naive/greedy algorithm might apply maximum torque to the rotor to extract maximum power for a moment, but this strategy will try to stall the rotor. As power is torque * angular velocity, both terms require consideration.
Thanks for your reply. We have a USB-powered current loop interface for the Teletypes; that's your design, I assume? If so, cool.
I figured it would be controversial to call the power supply a switching power supply, but I haven't seen a solid reason yet to exclude it. Putting a transformer upstream of the switching makes it an on-line power supply as opposed to an off-line power supply (dumb names, but I didn't make them). I'm not sure how you're distinguishing between a "switching voltage regulator" and a "switching power supply".
Oh, did you get the ones Steve Garrison makes up? That's my design. Or did someone else get the files off Github and make some?
A switching power supply has actual power conversion driven by the switching. See The Art of Electronics, by Horowitz and Hill, 3rd ed., section 9.6.
That thyratron circuit is a lamp dimmer circuit repurposed as a voltage regulator. Like SCRs and triacs, a thyratron is a switch you can't turn off. You have to wait for the input power to turn off. Usually that's the next cycle of AC. Because you can't turn off the power, you can't generate inductive spikes, so you can't pull the basic trick that make a switching power supply go.
There were some real switchers in the tube era. The most common one was used to generate the high voltage (10KV-20KV) for CRTs. Those used the horizontal oscillator, running at 15KHz and yanking the beam back at the end of each scan line, as a spike generator. That approach used a real vacuum tube, not a cold-cathode gas filled tube like a thyratron. So those were high voltage but low current devices.
Switching power supplies with serious current output had to wait for a component that could turn off fast under load. Power MOSFETS, etc. If you could do that with a thyratron, we would have had switching power supplies by 1950.
"I put the design on Github as open source and made a few for myself, and I've sold some board kits. Not enough potential volume to have it manufactured." - you could possibly have a look at services like macrofab etc. I used them to fab/assemble a single PCB not too long ago, which I was really pleased with.
Can't vacuum tubes such as krytrons still provide the ability to switch vast amount of current in the order of kiloamperes at kilovolts, which would be hard to use semiconductors for?
Apparently they were used in atomic bombs for delivering power to exploding-bridgewire detonators iirc.
The krytrons I've seen are too small to conduct that much current. The Wikipedia article refers to kiloampere currents ( https://en.wikipedia.org/wiki/Krytron ) but I don't see how that would work with the tube in their photograph. At long duty cycles you'd either vaporize the electrodes or fuse the wires, and at short duty cycles the parasitic inductance would be the limiting factor.
https://nuclear-knowledge.com/detonators.php provides more information, they are designed for fast switching, but still at vast currents re. triggered spark gaps "Typically, compact versions of these devices rate at 20-100 KV, and 50-150 kiloamps, and the triggering potential is one-half to one-third the maximum voltage. Switch current rise times last 10-100 nanoseconds. "
For krytron's specifically it says 'These devices have maximum voltage ratings from 3 to 10KV, and peak current rating of 300-3000 amps' which would have been useful for detonating the exploding-bridgewire, which requires a hefty current.
Good question. It's one of the recommended ones on the LT3750 data sheet.[1] I needed to charge up 2uF to 120V in 13ms or less, and the smallest of the Coilcraft transformers listed could do that. Matching controller, transformer, and MOSFET is a big headache; subtle properties of all of them matter. That data sheet is a good read.
Finding the right MOSFET was a huge headache. I kept trying reasonable ones in LTSpice, then on a real board. Gate capacitance of the MOSFET really matters. You normally think of MOSFET gates as drawing nearly zero power, but in a switcher, you want to turn them on fast, which means pumping in almost an amp for a few nanoseconds.
That IC is intended for charging up photoflash units. I'm using it at a lower voltage with a lower capacitance but a faster cycle time. The examples show charge times around 1 second; I only have 22ms. I'm only charging 2uF. It's two 1uF ceramic caps; none of the current limits of electrolytic caps. Not surface mount, though; I tried those new ceramic multilayer surface mount capacitors, but they have some very strange properties; the capacitance declines with voltage. OK in filters, terrible for energy storage.
It took me seven boards to get this working. The first few were a much simpler design with a 555 timer running the switcher. It worked, but it turned out I needed 2uF instead of 1uF because the Teletype selector magnet has an inductance larger than the ham community thought it did. The simpler design couldn't charge up 2uF in 22ms (one bit time); it took about 30-35ms. I had to start over with a more efficient design. This is all running off a USB port, so there's a limited power budget.
Running off USB port power added of complexity. There are strict rules about drawing power from USB ports, and if you violate them, even for a microsecond, the USB port turns off, and on many devices stays off until power cycled. That's a good thing; it's why hot-plugging works. The AP2553W6 manages startup current draw and has comparators checking for abnormal situations. It has a reverse current flow detector. Spikes from the switcher made it back into the power input and tripped the AP2553W6's protection. Had to add another surface mount ferrite bead, L1, to damp out current spikes. A lot of switcher design is about putting small capacitors and inductors in the right places to damp out trouble. Most of this you can see in LTSpice.
What you don't see in LTSpice is the effect of board layout. LTSpice assumes idealized wires with zero resistance, capacitance, inductance, and coupling. The layout around U1 really matters. First time around, I didn't follow the recommended layout, and the system would not oscillate.
The LTSpice model is on Github, along with the KiCAD files, so you can play with the parameters.
20 years ago I visited the Energetica museum in Amsterdam. One of the exhibits was a large cart/trailer that was used to charge submarines from the WWI era (!). It had two HUGE hand-blown glass mercury rectifiers in the front of it; you could fit a small person inside each, and there was a couple inches of mercury sitting at the bottom.
I was shocked when a docent walked over and turned it on. The rectifiers lit the whole room up with a beautiful purple glow. Beautiful.
Doing a quick web search it looks like the museum is no longer. Too bad - even though I couldn't read the plaques, it was still one of the most fascinating museum experiences I've ever had.
The early days of radio are just as fascinating with plenty of big electronics for transmitters. Droitwich the BBC's main LW transmitter is 500kW and still uses some of the old, water cooled valves. Thanks to the last round of govt budget cuts the transmitter won't last beyond the last stock of those valves.
If you want to see that sort of thing in the SF Bay Area, visit the Marine Radio Historical Society in Marin.[1] They have a big ship-to-shore station, built on Federal land a century ago and turned over to the Park Service when it shut down.
They operate many of the transmitters each weekend. They applied to the FCC for a commercial coast station license, probably the last one, and got it.
So they can send at quite high power. They talk to museum ships around the world.
The Isle of Man Electric Railway had a huge mercury vapor rectifier in active use until 2010.[1] I saw it in operation once. It would glow brightly when the trams were drawing high power.
Tons of UV, that's how legacy fluorescent lamps work, a nice intense UV flux excites the phosphors inside the tube. The UV can't escape the glass but the white light from the phosphors certainly can. Germicidal lamps use UV-transparent quartz.
As for x-rays the typical voltage drop across a long tube is like 100 volts, the whole point of a ballast is matching the normal hundred or so volt drop to whatever your local line voltage is using at a constant controlled current. Anyway the penetrating power of an xray is linked to the voltage drop, so it would be difficult even theoretically to generate xrays stronger than a hundred volts or so. So given that it takes 50 KV to 100 KV for a dental xray source to beam completely thru a head, you're looking at like a thousandth the penetrating power. Very hand wavy estimate that 100 volt xray source will likely not penetrate the glass and almost certainly not penetrate clothing or the surface layer of dead skin and skin oils.
The risk assessment for being nearby a heavy cloud of vaporized hot mercury would seem to imply the main risks would be biochemical in nature not physics in nature. Actually the most realistic risk is an economic death penalty if that leaks and requires hazmat cleanup.
Probably not mercury rectifiers or thyratrons, but hydrogen and deuterium thyratrons do (edit - emit X-rays, that is). They're much higher voltage devices. Example at [1]
AFAIK, x-rays are the result of electrons slamming into metal at high speed from a high voltage accelerating potential (>20kV). The glow inside Mercury rectifiers comes from ionization of Mercury vapor. Various other voltage regulator tubes glow from the ionization of low pressure gases inside the tube.
Common beam power tubes and power pentodes sometimes glow blue from residual gas in the tube even with plate potentials ~500V.
Thyratrons were the early form of SCR, the silicon controlled rectifier. These aren't SMPS's in the sense we think of them today but they do switch the input at a controlled rate to create a controlled output so the nomenclature can be used in this sense. The proper term is: Phase-fired controller: https://en.wikipedia.org/wiki/Phase-fired_controller
You can see the idea is to run a timer that is phase locked to the incoming mains frequency. Now you can control when the switches turn on during a half cycle. If you turn the switch on at the beginning of a half cycle, you have full power. If you turn the switch on midway through the cycle, you get half power and so on. So your command signal asks the controller for more and more of the complete wave cycle until you get the full RMS value of the line voltage plus the load current (minus the losses in the rectifiers of course). The resultant output is a chopped up EMI laden mess but it does the job quite nicely after some filtering.
They were also used in early motor drives to control the speed of a brushed DC motor from single or three phase AC source. I know some lathes from the 50's or 60's had thyratron motor drives in them.
At my work we have an Electron beam welder which uses an SCR controller for the high voltage power supply. It's interesting: the controller is directly fed 480V three phase. From there in comes in through a breaker, a contactor, and two current sensing transformers.Like so (dammit variable width fonts...):
A--~~--||--S--^^^^^^--/--SCR---\---)
B--~~--||-----^^^^^^--|-BRIDGE-| )Inductor
C--~~--||--S--^^^^^^--\----------/---)
Key: ~~ fuse, || contactor, S current sensor, ^^^^^^ transformer primary
The three phases then run to the power three supply transformers in series and then off to a three phase SCR bridge for a total of six SCR's. The output of the bridge has a huge 200 pound inductor across it. The idea is the bridge is phase fire controlled and the inductor is so high in value that the controller can slowly watch the current ramp when the SCR's are turned on and wait until the feedback from the power supply matches the command from the potentiometer and adjust the phase angle firing accordingly. It's creating a controlled short circuit using the series transformers as the load. It's a primitive solid state method of varying an AC voltage. Before the SCR system they used a motor generator with an op-amp PID loop watching the feedback and control pot who's output controlled a small phase fired SCR bridge that delivered a varying DC voltage to the generator field winding. You effectively had a motor generator who's output varied from 0-480V AC three phase. Today you'd have a small metal oil tank containing an entire SMPS which is smaller than the control cabinets for our old linear supplies.
Mercury rectifiers are beautiful. I once built a vacuum tube audio amplifier with directly heated triodes and mercury rectifiers, aiming for a symmetrical orange-blue-blue-orange glow.
It turned out that mercury rectifiers make a lot of electrical noise when they switch, so there was an annoying 120 Hz buzzing noise. But it did look cool.
I recently built a "vacuum tube nightlight" (http://www.electronixandmore.com/projects/vrtubenightlight/i...) because I thought the plasma tubes give off such a nice glow. But they aren't very bright and it's hard to see the plasma; these rectifiers are way more attractive but I can't bring myself to work with them.
> these rectifiers are way more attractive but I can't bring myself to work with them.
Cool project! Do you say you can't bring yourself to work with them for safety reasons (as in, I imagine mercury vapor is very dangerous if it escapes the tube) or is there another reason?
Using controlled rectifiers like this usually isn't regarded as a SMPS, though. (Notably because this technique does not allow to select the switching frequency, which is fixed by the grid in this circuit, so this circuit does not allow high-frequency switching, which is one of the main reasons SMPSs are much lighter than traditional power supplies -- the higher frequencies mean a much smaller core can be used while avoiding saturation).
Using SCRs or triacs to pre-regulate the voltage of a linear regulator was a very common technique well into the late 80s for high power, precision power supplies. The power supply shown here works very much the same, except there being no linear post-regulation stage.
Contrast this with the HV generation in devices using CRTs, which early on (~50s) started to use high-frequency converters, usually of the resonant kind.
This is not a switched-mode power supply (SMPS), sorry.
This is more like a vacuum analog of the SCR.
Switching on and off based on phase angle isn't the same thing as the working principle in SMPS's.
An SMPS, in a nutshell, uses pulses of current to "charge" an inductor, which continues to source current during the off periods when the current pulse is cut off and the magnetic field is collapsing. (Inductors oppose changes in current.)
There is also non-inductive SMPS using capacitors only: the charge pump.
> An SMPS, in a nutshell, uses pulses of current to "charge" an inductor, which continues to source current during the off periods
That's exactly what happens in this power supply. The tubes charge up a giant (grapefruit-sized, if grapefruit were cubes) inductor, which supplies the current when the thyratrons aren't.
I don't see a good reason not to consider this a switching power supply. Phase angle is just PWM at a lower frequency.
Whether this qualifies as a switching supply is an interesting question. I don't think I agree with Animats in that regard. Regulation is accomplished by switching a nonlinear element via a feedback loop, and that's good enough to qualify it as a "switched-mode" supply in my book.
You certainly couldn't call it a linear regulator, because the thyratrons are either fully on or fully off at all times. From the input's point of view it will exhibit negative resistance, with a reduction in the current required as the input voltage rises. That makes the classification especially hard to refute.
It's true that energy is being stored in the smoothing choke, but that alone doesn't make the difference since the choke could be used to accomplish the same thing in a traditional linear supply. The choke isn't inside the feedback loop, though, and that is a point in favor of the "It's not a switcher" camp. But it's the only one. In any event, charge-pump supplies don't need an inductor at all, and nobody questions whether they operate in linear or switched-mode.
(Edit: looking at the schematic, the filter choke is indeed inside the feedback loop. Case closed, it's a switching supply.)
The power supplies I worked with on the Model 28 were the typical linear design. They had huge resistors on them that after a while, the heat from them would lift the copper pads off the circuit card. So they'd be hanging off the card, only held on by their solder connection. If the inspectors took a dislike to us, they'd write us up for them. But mostly they knew this was a design "feature" and would overlook it.
One of the cool things about that era of Teletype was the mechanical serial to parallel converter. This was a multi-lobe camshaft that as the pulses came in and the electromagnet selector engaged/released, would (if your timing was set right) select five bars (for your Baudot code) that controlled the position of the type box where all the letters and numbers were.
Yes, the usual Teletype loop current supply is a 120VDC supply with a 10K 2W resistor, to get 60mA constant current. Efficiency is below 10%, with over 90% of the power going to heating the resistor.
That's partly why I built a switching supply interface. Far less heat. Small box, no ventilation required.
I briefly considered taking one of the cards along to my high-reliability soldering class just to provoke a reaction from the instructor.. But figured it might bring down attention from On High into the state of our circuit cards and that wouldn't have been good. Besides, they lasted 5+ years like that before needing replacement. We pretty much only replaced them when the boards became brittle from the heat.
I had no inkling I needed a mercury thyratron until now! Amazing stuff, this is like something from Fallout brought to life, and the mercury makes it suitably hazardous. I'm guessing the mercury is integral to the hue?
I saw something like this in a railway museum in Yorkshire or thereabout when I was a kid - I recall its label included 'rectifier' and I think it contained mercury, and was flashing or sparking in some way. I guess it must have been one of the mercury rectifiers as already mentioned, though I don't remember it glowing quite so beautifully. Certainly had me intrigued.
There are a lot of comments here saying that this isn't a SMPS, then proceed to describe a flyback converter (and the difference vs this unit) as a justification. Just note that the field of power electronics is quite large, and as an example, some power converters don't even have an inductor or transformer (though most do).
As I understood, the definition of a SMPS relates to switching between discrete states (i.e. on/off) as opposed to a linear supply, which dissipates power to regulate.
Source: am a power electronics engineer.
I've been following curiousmarc's channel for a couple years. I love his videos. This teletype restoration is amazing. The most recent video on his channel is of him and the guys going to a place that sells replacement parts... for teletypes. I mean this guy they visit literally has every part you would need to repair, and probably build teletypes from scratch. They had everything Marc needed to complete his restoration. Amazing!
> capacitors are still the bulkiest components in the MacBook charger, as you can see below.
This seems like an odd statement, given the image directly next to that sentence (and all evidence from any electronics device I've ever taken apart). The transformer is the largest piece, followed possibly by the inductors. IANA electrician, though, so maybe there's some context that I'm missing (i.e. a transform isn't technically a single component)?
Wow, never thought to look at the PS when I played with one of these at the university ham club station back in the 80's. Now I wonder what other cool stuff I missed.
As someone pointed out, that's a switching voltage regulator, not a switching power supply. The transformers there are all upstream of the switching.
I've restored five Teletype machines like the OP's Model 19 [1], so I've needed similar 120VDC 60mA power supplies. So I designed my own switching power supply.[2] This has a USB port for input, and a 120VDC 60mA output for directly driving the Teletype machine. It's powered entirely from the USB port.
This seemed impossible to some people. There's only 5V at less than 500mA coming in, and 120VDC 60mA out. But it's not impossible, because the load is inductive and intermittent. The selector magnet in old Teletypes has a huge inductance, about 5.5 Henries. (Not mH, H.). The 120VDC is only needed for about the first 1ms of each bit time, to force current through that huge inductance. By 5ms or so, you only need about 6V. So you can charge up a capacitor to get the initial 120V, then let a sustain supply take over.
My design is totally modern, built from surface mount components and in a small case. Here's the schematic.[3] There's an explanation in [2].
It's been amusing to see the reaction of the Teletype community. They like it, but most can't solder surface mount. One hobbyist is making these things for others. I put the design on Github as open source and made a few for myself, and I've sold some board kits. Not enough potential volume to have it manufactured.
Informally, here's how a switching power supply works. Everywhere else in electronics, you try to get rid of spikes. In switching power supplies, you make and use big ones. You start with a source of DC power, and you hook that to the primary winding of a transformer, with a switch so you can turn the power on and off. You turn the switch on, and current flows into the transformer. The magnetics in the transformer charge up, storing energy. After a while (milliseconds) the magnetics will saturate, and can't store any more energy. You now have a short circuit, DC going through a low-resistance transformer. But you turn off the switch before that happens. (Switching power supplies are always milliseconds from burnout, which is why they burn up if the switching fails.)
When you turn the switch off, you now have an open circuited inductor. The energy in that inductor has to go someplace. It comes out as a huge spike, in theory infinite voltage if the transformer resistance was zero, and in practice it can be a few hundred volts. It can't come out the primary, because the switch is open. So it comes out the transformer's secondary winding, where it's fed through a diode into a capacitor. There's the output.
It's simple. An old-style auto ignition with a coil and breaker points works this way. The problems come in as you make it well-behaved. First, controlling the switch is complicated. You want to open the switch before the transformer hits saturation. Failure to do this will burn something out. So there's usually current sensing. Then you want to turn the switch back on when the output voltage from the inductor drops below the voltage in the output capacitor, because no more current will flow through the diode after that.
That just makes it output power. Then you need output voltage sensing, which shortens the charging time to reduce output to maintain the desired voltage. You need protection to shut everything down if the switch gets stuck. (MOSFETs tend to fail in the ON state, and lack of good protection circuitry causes fires.)
This thing works by making big spikes at a few hundred kilohertz. That makes it a radio transmitter. You need inductors and bypass caps to prevent it from blithering all over the RF spectrum. Or sending spiky noise to its output or input. The bypass caps and inductors need to be close to the source of the spikes, so PC board layout really matters. These things will not work on a breadboard.
All this is why switching power supplies have so many small parts. Once you get it right, they work beautifully. Very high efficiency and low heat.
[1] http://www.aetherltd.com [2] https://github.com/John-Nagle/ttyloopdriver [3] https://raw.githubusercontent.com/John-Nagle/ttyloopdriver/m...